Estrogen effects on the tuberoinfundibular dopaminergic system in the female rat brain

Estrogen effects on tyrosine hydroxylase (TH), monoamine oxidase types A and B (MAO), and dopamine (DA) in microdissected regions of the hypothalamus, preoptic area and substantia nigra (SNR) of the female rat brain were investigated. Ovariectomized (OVX) young adult female rats were implanted with single silastic capsules containing 100% estradiol valerate (EV). Control rats received empty silastic capsules. Two weeks following capsule insertion, EV decreased TH activity and DA concentration in the arcuate nucleus (AN) while no significant changes in TH activity or DA concentration were observed in the SNR, ventromedial nucleus (VMN), suprachiasmatic nucleus, paraventricular nucleus, medial preoptic nucleus, or the periventricular preoptic nucleus. Although estrogen suppressed TH and DA in the AN, 2 weeks following removal of the estrogen containing capsules, TH activity and DA concentration were restored to control (OVX) levels. Suppression of MAO activity occurred in both the AN and the VMN of rats implanted with EV capsules and returned to OVX levels following the removal of the estradiol load. These results revealed that estrogen effects on TH and MAO activities and DA concentration in the midbrain are region specific and reversible; and that among the dopaminergic systems studied, estrogen effects on TH and DA are confined to the tuberoinfundibular dopaminergic system (TIDAS). Furthermore, these results support our hypothesis that estrogen is a key regulator of DA function in the TIDAS via effects on TH. The importance of these findings to the control of gonadotropin secretion and reproductive cyclicity is discussed.     

Brain catecholamine content during the estrous cycle and in steroid-primed rats

Norepinephrine (NE) and dopamine (DA) levels were measured in several estrogen concentrating brain regions over the estrous cycle and in steroid-primed ovariectomized rats under experimental conditions used to study sexual receptivity. Norepinephrine content in the ventromedial hypothalamus (VMH), lateral septum (LS) and medial preoptic area (POA) varied during the estrous cycle. The highest NE levels were found during metestrus in these brain regions. In the ovariectomized rat, NE levels were increased in the POA and LS 12 hours (hr) after the injection of 3 micrograms of estradiol benzoate (65% and 33%, respectively). Norepinephrine content in the POA and LS remained elevated 24 hr and 48 hr (0.5 mg progesterone at 42 hr) after treatment but were not different from control levels at 96 hr. Dopamine concentrations were not significantly altered over the estrous cycle or by the administration of estradiol benzoate in any of the brain regions studied. These results suggest that estrogen may selectively alter noradrenergic activity in brain regions that are implicated in the control of sexual receptivity and/or ovulation.     

Variations of monoamines and their metabolites in the human brain putamen

The levels of the monoamines dopamine (DA), serotonin (5-HT) and norepinephrine (NE) and the monoaminergic metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were measured with HPLC-ECD in 42 samples from human brain putamen. The influence of gender and of age was investigated and correlations between the monoamines were established. The DAergic system shows a significant difference between males and females, with females having lower DA and higher DOPAC levels and a higher DOPAC/DA ratio than males. No gender-related differences of 5-HT and its metabolites were observed, nor of NE. Three different age groups (group 1: 0–9.9 years; group 2: 10–59.9 years; group 3: 60 years and older) were defined according to previous studies on ontogenesis and senescence in human brain. An increase in 5-HT levels, decrease in 5-HIAA levels a d a decrease in the 5-HIAA/5-HT ratio were observed after the first decade of life. Changes in the DAergic system were seen in senescence, with decreasing DA levels and an increase in the HVA/DA ratio. DOPAC, HVA and the DOPAC/DA ratio are unaffected. NE is similar in all age groups. The analysis of the relation of the levels of the three monoamines proved a strong correlation between the DAergic and 5-HTergic systems. The nature of this relationship might have an impact on neuro-psychiatric disorders and brain function.     

Sex differences in cytosolic progestin receptors in microdissected regions of the hypothalamus/preoptic area of guinea pigs

Cytosolic progestin receptors (CPRs) were measured in microdissected nuclei of the hypothalamus and preoptic area of male and female guinea pigs. Adult gonadectomized animals were given 3 daily injections of 20 micrograms/day estradiol benzoate (EB) or oil vehicle. 24 h later, animals were sacrificed and cytosolic progestin receptors were measured using the synthetic progestin 3H-R5020. CPR levels did not differ significantly between oil treated males and oil treated females in any brain areas examined. With EB treatment, males showed significant increases in CPRs in most of the brain areas in which females showed increases, i.e. in the medial preoptic area, the periventricular part of the preoptic area, the periventricular part of the anterior hypothalamus, the ventromedial nucleus of the hypothalamus, the periventricular part of the medial hypothalamus and the arcuate-median eminence. However, EB treated males showed significantly lower CPR levels than EB treated females in both the periventricular part of the preoptic area and the periventricular part of the medial hypothalamus.     

Monoamine Levels and Turnover in Brain: Relationship to Priming Actions of Estrogen

Norepinephrine (NE), dopamine (DA) and serotonin (5HT) levels and turnover rates were studied in 8 discrete brain nuclei of ovariectomized rats 24 hours after the administration of 5 microgram of estradiol benzoate (EB) or sesame oil vehicle. This estrogen paradigm, by itself, did not induce sexual behavior or alter LH levels at the time these parameters were evaluated. However, combined with progesterone, the estrogen treatment was sufficient to generate an LH surge and induce sexual receptivity. Steady state concentrations of NE were significantly higher in the diagonal band of Broca (NDB) and the periventricular nucleus (PVE2; anterior hypothalamic level) following EB treatment. In addition, 5-hydroxyindole acetic acid (5HIAA) concentrations were elevated in the dorsal raphe of EB treated animals. Estrogen did not affect steady state concentrations of DA or 5HT in any of the brain nuclei studied. Turnover rates (K, pg/microgram protein/hr) and rate constants (k, hr-1) for NE were increased in the lateral septum (K, 140%; k, 120%), NDB (K, 160%; k, 130%) and the PVE2 (K, 140%; k, 70%) in EB treated animals. Estrogen decreased the rate constant for NE by 30% in the medial preoptic area. In contrast, DA and 5HT turnover rates were not significantly affected by estrogen. These results localize sites where estrogen induces changes in noradrenergic activity and suggest that these changes may be involved in the priming action of the steroid in inducing sexual behavior and/or gonadotropin secretion.     

Effects of capsaicin on central monoaminergic mechanisms in the rat

Summary The acute and chronic effects of capsaicin (s.c.) on the monoamines in the preoptic region + hypothalamus (RPO-H), spinal cord, substantia nigra and striatum were studied. Levels of DOPA, DA, DOPAC, HVA, 3-MT, NA, Trp, 5-HTP, 5-HT and 5-HIAA were determined by means of liquid chromatography (HPLC-EC). In response to acute capsaicin treatment, the levels of DA, DOPAC and DA synthesis rate (DOPA formation) were increased in a dose-dependent manner in the RPO-H and spinal cord. The disappearance rate of NA was accelerated in both regions. In substantia nigra, increased DOPAC levels were found whereas the levels of 3-MT were decreased in striatum after acute capsaicin treatment. Only minor changes on the levels of 5-HT and 5-HIAA in the regions studied were noted. Neonatal or adult capsaicin treatment failed to affect the levels of NA, DA and 5-HT (measured two months or five weeks after injection, respectively) in the regions studied. A capsaicin injection to rats pretreated with the drug as adults did not affect either the monoamines in the RPO-H and spinal cord or the body temperature. In contrast, in rats pretreated with capsaicin as neonates, a second injection of the drug to adult animals elicited hypothermia and changes in monoamines similar to those observed in naive animals.     

Pineal melatonin and brain transmitter monoamines in CBA mice during chronic oral nicotine administration

The effects of chronic oral nicotine administration on the pineal melatonin and brain transmitter monoamines were studied in male CBA mice, which possess a clear daily rhythm of melatonin secretion. On the 50th day of nicotine administration, pineal melatonin as well as cerebral dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined at various times. The chronic nicotine treatment did not alter the timing of the pineal melatonin peak, which occurred at 10 h after the light offset. However, in mice drinking nicotine solution, the nocturnal pineal melatonin levels were lower than in control mice drinking tap water. The chronic nicotine treatment increased the striatal DA, DOPAC, HVA and 5-HIAA levels, the hypothalamic NE, MHPG and 5-HIAA and the cortical MHPG. Most prominent effects of nicotine were found at 8 h after the light offset, when the striatal levels of DA and HVA, hypothalamic NE and MHPG as well as cortical MHPG were significantly elevated in the nicotine-treated mice compared with the control mice. No direct correlation between nicotine's effects on brain transmitter monoamines and on pineal melatonin levels was apparent. The results suggest that chronic nicotine treatment slightly suppresses the melatonin production but does not alter the daily rhythm of pineal melatonin in mice maintained on a light-dark cycle. However, the results indicate that nicotinic receptors might be involved in the regulation of pineal function.     

Estradiol modulation of central monoamine activity in female mountain spiny lizards

Although estradiol (E2) mediates many behaviors in females, relatively little is known about its role in female aggression. Previous studies in female mountain spiny lizards indicated that female aggression is modulated by ovariectomy and sex steroid hormone replacement and that expression of aggressive behavior is accompanied by changes in serotonin activity. This study examines if E2 modulates the activity of serotonin and other central monoamines. Free-living females were caught and housed in the laboratory and received one of 3 treatments: sham surgery (SHAM), ovariectomy plus empty implant (OVEX), or sham surgery plus a long lasting E2 implant (E2-IMP). After 3 weeks of treatment, selected brain areas were examined for levels of monoamines and their metabolites. Changes in monoamine activity were most pronounced in the septum where levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine (NE) were higher in E2-IMP females relative to SHAM, and levels of 5-HIAA were higher in OVEX females relative to SHAM. Changes in dopamine (DA) activity were also found, with increased DA concentration and decreased ratio of forebrain:brainstem HVA concentrations in E2-IMP relative to SHAM females. These results suggest that the actions of E2 on aggression might be mediated, in part, by dose-dependent effects on 5-HT activity in the septum.     

Specificity of interleukin–1β-induced changes in monoamine concentrations in hypothalamic nuclei: blockade by interleukin-1 receptor antagonist

The purpose of this study was to examine specificity in the effects of interleukin-1β (IL-1β) on monoamines in various areas of the hypothalamus. Adult male rats were injected i.p. with saline or 2.5 or 5.0 μg of IL-1β or were pretreated with 500 μg of IL-1 receptor antagonist (IL-1ra) followed 5 min later by 5 μg of IL-1β. The paraventricular nucleus (PVN), arcuate nucleus (AN), median eminence (ME), and medial preoptic area (MPA) were microdissected and analyzed for neurotransmitter concentrations by high-performance liquid chromatography with electrochemical detection (HPLC-EC). In the PVN, IL treatment produced significant increases in the concentrations of norepinephrine (NE), dopamine (DA), DA metabolite dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and its metabolite 5-hydroxyindoleacetic acid (5-HIAA). IL-1 treatment increased the concentrations of NE and DA in the AN but only of NE in the ME, and it was without any effect in the MPA. Pretreatment with IL-1ra completely blocked the IL-1 effects. It is concluded that IL-1 induces highly specific changes in monoamine metabolism in the hypothalamus, and the nature of these changes depends on specific hypothalamic nuclei.     

Dorsal lesions of the prefrontal cortex: effects on alcohol consumption and subcortical monoaminergic systems

Male Wistar rats were subjected to either bilateral aspiration lesions of the dorsal regions of the prefrontal cortex (PFC) or sham lesions and placed on a 6-week, modified sucrose-fading procedure. At the time of sacrifice, the size of the lesion, both in anterior-posterior and medial-lateral dimensions, was measured. Following sacrifice, levels of dopamine (DA), serotonin (5-HT), norepinephrine (NE), and their metabolites were measured in the midbrain (raphe) and nucleus accumbens (NA). Lesioned animals had reductions in 5-HT in the NA, and DA and NE in the raphe. The lesioned group drank more of a solution of 5% alcohol than controls early in the sucrose fading, and less during the later stages. In the lesioned group, the size of the left- and right-hemisphere lesions predicted 5-HIAA levels in the NA, and 5-HT and 5-HIAA levels in the raphe. A laterality effect was noted, such that the size of left-hemisphere lesions were positively associated with raphe 5-HT and 5-HIAA levels, and negatively associated with 5-HT levels in the NA, while right-hemisphere lesions showed the opposite relationships. In addition, the width of the left-hemisphere lesion predicted some measures of alcohol intake. These results suggest that, in the rat, the dorsal PFC is involved in the regulation of monoamines in subcortical regions known to be important in the regulation of reinforced behaviors, and that this regulation differs between hemispheres and shows a laterality effect. In addition, the dorsal PFC appears to have a subtle involvement in the regulation of alcohol intake.     

Changes in cortical and subcortical levels of monoamines and their metabolites following unilateral ventrolateral cortical lesions in the rat

Suction lesions were made in the anterior, posterior or both halves of the right ventrolateral cortex in rats. Six days later, levels of the monoamine neurotransmitters, norepinephrine (NE), dopamine (DA) and serotonin (5-HT), and their metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in cortical and subcortical regions of lesioned rats and compared to values in sham-operated animals. NE and 5-HT were decreased in sections of ipsilateral (right) cortex including, and posterior to lesions, while 5-HIAA was increased throughout the ipsilateral cortex. Decreases in monoamines and increases in metabolites and metabolite:monoamine ratios (especially 5-HIAA:5-HT) were found in ipsilateral subcortical structures, including striatum, nucleus accumbens, hippocampus, hypothalamus, midbrain and brainstem, depending on the type of lesion. Subacutely, focal ventrolateral cortical lesions may profoundly alter the levels and utilization rates of monoamine neurotransmitters in widespread regions of the ipsilateral hemisphere.     

Activity Wheel Running Reduces Escape Latency and Alters Brain Monoamine Levels After Footshock

We examined the effects of chronic activity wheel running on brain monoamines and latency to escape foot shock after prior exposure to uncontrollable, inescapable foot shock. Individually housed young (∼50 day) female Sprague-Dawley rats were randomly assigned to standard cages (sedentary) or cages with activity wheels. After 9–12 weeks, animals were matched in pairs on body mass. Activity wheel animals were also matched on running distance. An animal from each matched pair was randomly assigned to controllable or uncontrollable inescapable foot shock followed the next day by a foot shock escape test in a shuttle box. Brain concentrations of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were assayed in the locus coeruleus (LC), dorsal raphe (DR), central amygdala (AC), hippocampus (CA1), arcuate nucleus, paraventricular nucleus (PVN), and midbrain central gray. After prior exposure to uncontrollable foot shock, escape latency was reduced by 34% for wheel runners compared with sedentary controls. The shortened escape latency for wheel runners was associated with 61% higher NE concentrations in LC and 44% higher NE concentrations in DR compared with sedentary controls. Sedentary controls, compared with wheel runners, had 31% higher 5-HIAA concentrations in CA1 and 30% higher 5-HIAA concentrations in AC after uncontrollable foot shock and had 28% higher 5-HT and 33% higher 5-HIAA concentrations in AC averaged across both foot shock conditions. There were no group differences in monoamines in the central gray or in plasma prolactin or ACTH concentrations, despite 52% higher DA concentrations in the arcuate nucleus after uncontrollable foot shock and 50% higher DOPAC/DA and 17% higher 5-HIAA/5-HT concentrations in the PVN averaged across both foot shock conditions for sedentary compared with activity wheel animals. The present results extend understanding of the escape-deficit by indicating an attenuating role for circadian physical activity. The altered monoamine levels suggest brain regions for more direct probes of neural activity after wheel running and foot shock.     

Dynamics of noradrenergic circadian input to the chicken pineal gland

To analyze the dynamics of sympathetic input to the chicken pineal the concentrations of catecholamines, indoleamines and some of their metabolites were determined by high performance liquid chromatography with electrochemical detection (HPLC-EC) in the pineal glands of young chickens killed at different times of day. Rhythmic variations over 24 h were observed in tissue levels of dopamine (DA), 5-hydroxytryptamine (5-HT), N-acetylserotonin (NAS) and 5-hydroxyindoleacetic acid (5-HIAA), while norepinephrine (NE) concentrations exhibited no significant change. DA content peaked 2 h after onset of darkness and NAS was detectable only during the night. A bimodal pattern of 5-HT and 5-HIAA levels was observed with peak tissue levels occurring at dawn and dusk. To determine the possible differential effects of light on these biogenic amines, birds were sacrificed at midday, midnight and at midnight following a 1 h exposure to light, and their pineals processed for HPLC-EC. NE, DA and 5-HT levels were similar at midday and midnight, while 5-HIAA and NAS were elevated during the night. Midnight illumination decreased NE and NAS levels, increased 5-HT and 5-HIAA levels and had no effect on DA levels. Temporal variations in NE turnover were determined by pretreating young chickens with alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor, and measuring the rates of decline in NE content over 2 h at midday and midnight in birds held on light cycles and at mid-subjective day in birds held in constant darkness (DD).(ABSTRACT TRUNCATED AT 250 WORDS)     

Topographical dopamine and serotonin distribution and turnover in rat striatum

Topographic distribution of dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) was determined in rat striatum using high-pressure liquid chromatography (HPLC) with electrochemical detection. The ratios of DOPAC:DA and 5-HIAA:5-HT were calculated as indices of turnover of DA and 5-HT. There was a rostro-caudal gradient for both DA and 5-HT, with DA highest in rostral striatum and 5-HT highest in caudal striatum (P less than 0.01). DA concentrations in the coronal plane showed a homogeneous distribution except at the level of the globus pallidus. DOPAC also showed a rostro-caudal gradient and concentrations were significantly increased in the nucleus accumbens (P less than 0.01). DOPAC:DA ratios were significantly increased in both the nucleus accumbens and the ventromedial striatum as compared to the remaining striatal punches. 5-HT was more heterogeneously distributed in the coronal plane with concentrations highest in the ventromedial and the ventrolateral quadrants, where they were 2-3-fold higher than in dorsal striatum (P less than 0.01). Concentrations of 5-HIAA were highest in the nucleus accumbens and ventromedial striatum but HIAA-5-HT ratios were highest in the dorsolateral striatum (P less than 0.01). DA turnover is therefore highest in limbic innervated (n. accumbens and ventromedial) striatum while 5-HT turnover is highest in sensorimotor innervated (dorsolateral) striatum. These findings provide further evidence for functional compartmentalization within the striatum.     

Lipopolysaccharide-induced changes in monoamines in specific areas of the brain: blockade by interleukin-1 receptor antagonist

The purpose of this study was to examine the specificity in the effects of lipopolysaccharide (LPS) on monoamine concentrations in different areas of the brain and the involvement of interleukin-1 (IL-1) in the LPS-induced effects. Adult male rats were injected i.p. with saline, 10 micrograms/kg body weight of LPS, or treated with 250 micrograms of IL-1 receptor antagonist (IL-1ra) 5 min before and 2 h after LPS. Several brain areas including the hippocampus (HI), caudate putamen (CP), the hypothalamic paraventricular nucleus (PVN), arcuate nucleus (AN), median eminence (ME) and the medial preoptic area (MPA) were microdissected and analyzed for neurotransmitter concentrations by HPLC-EC. LPS treatment produced marked increases in the concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the PVN. In the AN, it increased DA concentrations and was without any effect on the MPA, ME, CP and HI. Treatment with IL-1ra in combination with LPS completely blocked the LPS-induced effects. It is concluded that LPS produces highly specific changes in monamine metabolism in the hypothalamus and that these effects are mediated at least in part by IL-1beta.     

Hypothalamic monoamines and their catabolites in relation to the estradiol-induced luteinizing hormone surge

Monoamines and non-conjugated catabolites (serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), norepinephrine (NE), and dopamine (DA] were measured in the medial basal hypothalamus (MBH) and preoptic area (POA) of ovariectomized (OVX) and OVX estradiol (E2)-treated rats using high-performance liquid chromatography with electrochemical detection. These E2 treatments were sufficient to induce an LH surge. The use of MHPG/NE ratios as estimates of NE release was validated in the rat hypothalamus by the major decreases of MHPG after injection of the alpha 2-adrenergic agonist, clonidine, and by MHPG increases after the alpha 2-antagonist, yohimbine. The ratio, MHPG/NE, decreased between morning and afternoon in the MBH but not in the POA; there were no differences between OVX and E2-treated rats. Previous studies using a variety of methods indicate that NE turnover increases during LH surges. The present data suggest that unconjugated MHPG is not a sensitive measure of NE release in the rat hypothalamus, but can detect the large changes produced by stimulating or inhibiting the alpha 2-adrenergic autoreceptor. The ratios of DOPAC/DA and 5-HIAA/5-HT in the MBH decreased consistently between morning and afternoon in OVX rats, with or without E2 treatment. This suggests that the release of DA and 5-HT decreases during the day regardless of steroidal milieu.     

Cellular mechanisms of acute estrogen negative feedback on LH secretion: norepinephrine, dopamine and 5-hydroxytryptamine metabolism in discrete regions of the rat brain

Rats on diestrous day 1 were ovariectomized (OVX) and killed 10 days later. LH was measured by RIA and the metabolism of NE, DA and 5-HT were assayed concurrently in the suprachiasmatic (SCN), medial preoptic (MPO), dorsomedial (DMN), rostral (ANr) and caudal (ANc) arcuate nuclei as well as the median eminence (ME) utilizing HPLC with electrochemical detection. Serum LH increased 10-12 fold 10 days following OVX compared to diestrous controls. The injection of estradiol benzoate (Eb, 20 micrograms in corn oil/rat, SC) did not affect LH concentrations at 30 minutes but decreased serum LH both 60 and 180 min following its administration. OVX caused an increased NE metabolism (estimated by the concentration of the NE metabolite, 3-methoxy-4-hydroxyphenylethylene glycol) in the SCN, MPO, ME, and DMN and a decreased NE metabolism in the ANc compared to diestrous control values. All of these changes were reversed or attenuated 180 minutes following Eb treatment. Observed changes in the DA and 5-HT neuronal systems were more restricted and less dramatic with the largest effects on DA metabolism occurring in the DMN and ME and the clearest changes in 5-HT metabolism occurring in the MPO, ANr, and ANc. The results demonstrate that the inhibition of LH secretion following the injection of Eb to OVX rats is accompanied by changes in metabolism in NE neurons in preoptic (SCN and MPO) and medial (ME, DMN, and ANc) hypothalamic areas, as well as in DA neurons in the DMN and ME, and in 5-HT neurons in the MPO, ANr, and ANc.     

The effects of himantane and cycloprolylglycine on the enzymatic linkage of monoamine synthesis in the rat brain

Using HPLC we studied the effects of new substances with antiparkinsonian activities, viz., himantane and cycloprolylglycine (CPG), on the contents of monoamines and their metabolites in the brain structures of Wistar rats under conditions of the inhibition of tyrosine and tryptophan hydroxylases. It was shown that 70 min after administration himantane induces a significant decrease in the level of noradrenaline in the nucleus accumbens (NA) and striatum. At 70 min after administration of CPG, we observed an increase in the DOPAC/DA ratio in the NA and the level of 5-HIAA in the striatum. At 24 h after CPG administration, we observed an increase in the HVA content and HVA/DA ratio in the hypothalamus and striatum. We found a decrease in 5-HIAA in all brain structures we studied at 24 h after administration of CPG, which was absent at 70 min after injection of the substance; the magnitude of 5-HIAA/5-HT decreased in the hypothalamus, nucleus accumbens, and hippocampus. Our results suggest that both substances we studied influence serotonergic transmission by inhibition of the MAO B enzyme.     

Spinal cord monoaminergic system response to age and cold-acclimatization in Muscovy duckling

Summary. The effect of age and cold acclimatization on the regional distribution of monoamines in duckling spinal cord was studied. In thermoneutral controls (TN), the high dopamine (DA) to norepinephrine (NE) ratios (0.25 at 4 weeks of age and 0.15 at 6 weeks of age) suggest the presence of specific (non precursor) dopaminergic pools in cervical spinal cord. DA levels and the ratio of DA to NE were lowered by age and cold exposure in the cervical cord. In TN ducklings, serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) showed a decline with age in the spinal cord, indicating that this system is affected with development, whereas cold exposure prevents this decrease. The contents of 5-HT (+58%), 5-HIAA (+93%) and the ratio of 5-HIAA to 5-HT (+50%) are higher in the cervical spinal cord of cold acclimated than in TN ducklings. These results indicate that central monoaminergic systems are markedly affected by age and cold exposure. Received November 11, 1999; accepted March 6, 2000     

Age-related changes in cytoplasmic estradiol receptor concentrations in microdissected brain nuclei: Correlations with changes in steroid-induced sexual behavior

The purpose of this study was to: (1) determine at what age changes in cytoplasmic estradiol receptors are evident in specific microdissected brain areas of the female rat; (2) assess whether alterations parallel previous changes observed when large brain areas were used for determination of receptor concentrations; and (3) assess whether changes in cytoplasmic estradiol receptors are correlated with changes in steroid-mediated physiological functions.To assess the effects of age on cytoplasmic estradiol receptor concentrations, we used virgin female Sprague-Dawley rats at 3–4 months, 7–8 months and 10–11 months of age. They were ovariectomized 7–14 days prior to use to allow maximal translocation of receptors to the cytoplasm. The animals were anesthetized and perfused with a 10% (v/v) solution of dimethylsulfoxide to protect the receptor proteins from the effects of freezing. Brains were removed and frozen. This procedure of freezing the brains caused a minimal (15–18%) loss in the number of receptors and no change in the dissociation constant. Consecutive 300 μm sections were sliced and the following nuclei and brain areas were microdissected: bed nucleus of the stria terminalis, suprachiasmatic-preoptic area, medial preoptic nucleus, periventricular preoptic nucleus, periventricular anterior hypothalamic area, paraventricular nucleus, dorsomedial nucleus, ventromedial nucleus, arcuate-median eminence, medial amygdala, and cortical amygdala. The pituitary gland was also removed and analyzed. The cytoplasmic fraction from a tissue pool from 3 animals was prepared and aliquots were incubated with [³H]estradiol at a final concentration of 1.5 nM in the presence or abssence of 100-fold excess moxestrol. Receptor-bound [³H]estradiol was separated from free hormone by gel filtration. There was no difference in cytoplasmic estradiol receptor concentrations in any brain area in 7–8-month-old rats compared to 3–4-month-old rats. In marked contrast, by 10–11 months of age, there was a significant decrease in the number of cytoplasmic estradiol receptors in the suprachiasmatic-preoptic area and medial preoptic nucleus with a similar trend in the bed nucleus of the stria terminalis and periventricular preoptic nucleus. These brain areas are included in the grossly dissected preoptic area used in previous studies. We observed an unexpected decrease in the ventromedial nucleus, but no change in the dorsomedial nucleus, paraventricular nucleus, periventricular anterior hypothalamic area or arcuate-median eminence, areas included in the grossly dissected medial basal hypothalamus.Since the ventromedial nucleus is involved in steroid-induced reproductive behavior we examined whether or not the decrease in cytoplasmic estradiol receptors in this area is correlated with behavioral changes. Young (3–4 month) and middle-aged (10–11 month) rats were ovariectomized and 1–3 weeks later, they received Silastic capsules which produced physiological levels of plasma estradiol. Two days later, 4 h before testing, rats received subcutaneous injections of progesterone. Proceptive behavior, lordosis quotient and lordosis quality score were assessed. Middle-aged rats showed significant deficits in all aspects of mating behavior. The data demonstrate that by 10–11 months of age, rats exhibit decreased cytoplasmic estradiol receptor levels in components of the preoptic area. The use of microdissection methods allowed us to detect changes in a particular component of the medial basal hypothalamus, the ventromedial nucleus. This was correlated with deficits in estradiol-induced behavior. The data suggest that changes in estradiol receptors may affect the ability of aging rats to respond to estradiol and may be a contributing factor to the age-related transition to acyclicity and infertility.